Radio Frequency Pretreatment Research Articles

Enhancing waste sludge solubilization through radio frequency treatment perforating bacterial cells

Sludge solubilization is known as a rate-limiting step of anaerobic digestion. Although radio frequency (RF) has been applied for sludge pretreatment due to its similar thermal effect as microwave, the potential non-thermal effects of RF treatment remain controversial. In this study, we demonstrate that RF pretreatment enhances the solubilization and lysis of sludge by 8.02%–19.69% through both thermal and non-thermal mechanisms with less energy input. Scanning electron microscope images provide direct evidence that RF-induced microcurrents penetrated bacterial cells, leading to the release of intracellular substances through formed pores. Additionally, the non-thermal effect of RF treatment which could weaken the cell protection and accelerate the lysis rate involves the disruption of binding forces between extracellular polymeric substances and microbial cells. On average, the utilization of RF at a frequency of 27.12 MHz demonstrates its efficacy as a sludge pretreatment technique, as evidenced by a 13.39% reduction in energy consumption and a 16.9% improvement in treatment performance compared to conductive heating (CH). The findings of this study elucidate the possible mechanism of RF treatment of sludge and could establish a theoretical basis for the practical application of RF treatment in sludge management.

Combining radio frequency heating and alkaline treatment for enhancement of sludge disintegration and volatile fatty acids production from anaerobic fermentation

Sludge pretreatment plays a crucial role in solubilizing particulate matters to release organic matter for subsequent anaerobic fermentation (AF). This study innovatively combines radio frequency (RF) heating and alkaline treatment, and finds that the combined pretreatment achieved a sludge disintegration rate of 35.11 %, which is 15.19 % and 8.48 % higher than single RF or alkaline pretreatment. The dissociated ions from the alkali are conducive to RF action on sludge. Furthermore, the combined pretreatment significantly benefits the subsequent AF experiments, resulting in a 9-fold increase in volatile fatty acids production. Considering cost-effectiveness, the optimal operating condition is a 10-minute RF treatment at pH 10 with a total cost of 4.35 × 10-3 dollars per kg soluble chemical oxygen demand (SCOD) increased. These findings provide a foundational basis for the development of a novel technology for sludge pretreatment.

Developing radio frequency pretreatment technology for improving yield and quality of flaxseed oil extractions

Flaxseed is considered as a major raw material for producing functional vegetable oil. To promote the extraction process of flaxseed oil, effects of radio frequency (RF) pretreatment at investigated temperatures (70, 90, 110, 130, and 150 °C) on yield, physicochemical property and sensory quality of flaxseed oil were determined. The results showed that the yield of flaxseed oil increased from 31.29 to 38.23% after RF pretreatment at 150 °C (p < 0.05). The total phenolic, lignan, antioxidant capacity, chlorophyll, and carotenoid contents of flaxseed oil increased significantly with the increase of RF pretreatment temperature (p < 0.05). Nonetheless, the higher RF pretreatment temperatures caused a slight increase on oil oxidation indices (free fatty acid, peroxide value, conjugated diene, conjugated trienes, and p-anisidine value). These results provide theoretical guidance for practical applications of RF pretreatment in the production and processing of edible vegetable oil.

Application of efficient pre‐treatment by physical fields for improving the taste and flavor of processed chicken enzymatic hydrolysate

In the condiment industry, people usually use enzymatic hydrolyzate to improve the umami of the product, and there are few reports on the umami intensity of the enzymatic hydrolysate. To explore the differences in taste and flavor of the samples pretreated with different physical fields, the chicken was pretreated by ultrasound (US, 600 W, 30 min), infrared radiation (IR, 90°C, 30 min), and radio frequency (RF, 120 mm, 30 min), respectively, and followed by a two-step enzymatic hydrolysis. Results revealed that the chicken enzymatic hydrolyzate after RF pretreatment (120 mm, 30 min) had the best overall taste and stronger umami. The sample treated with 90°C IR has a richer flavor, while there were no significant changes in taste of the 600 W ultrasound treatment group compared with the “control.” Therefore, RF pretreatment (120 mm, 30 min) is more suitable for industrial to produce low cost and high umami chicken enzymatic hydrolyzates. Practical applications In the condiment food industry, people usually use umami-rich enzymatic hydrolysates to improve the umami taste of products. The 120 mm plate spacing radio frequency pretreatment proposed in this study for 30 min before enzymolysis can significantly improve the taste characteristics of the chicken enzymolysate, significantly enhance its saltness and umami, and make the overall taste more harmonious. It provides a certain theoretical basis for the industrial production of low-cost umami-enhancing enzymatic hydrolysis products.

Effects of Radio Frequency Pretreatment on Quality of Tree Peony Seed Oils: Process Optimization and Comparison with Microwave and Roasting.

In this study, we explored the technical parameters of tree peony seeds oil (TPSO) after their treatment with radio frequency (RF) at 0 °C–140 °C, and compared the results with microwave (MW) and roasted (RT) pretreatment in terms of their physicochemical properties, bioactivity (fatty acid tocopherols and phytosterols), volatile compounds and antioxidant activity of TPSO. RF (140 °C) pretreatment can effectively destroy the cell structure, substantially increasing oil yield by 15.23%. Tocopherols and phytosterols were enhanced in oil to 51.45 mg/kg and 341.35 mg/kg, respectively. In addition, antioxidant activities for 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric-reducing antioxidant power (FRAP) were significantly improved by 33.26 μmol TE/100 g and 65.84 μmol TE/100 g, respectively (p < 0.05). The induction period (IP) value increased by 4.04 times. These results are similar to those of the MW pretreatment. The contents of aromatic compounds were significantly increased, resulting in improved flavors and aromas (roasted, nutty), by RF, MW and RT pretreatments. The three pretreatments significantly enhanced the antioxidant capacities and oxidative stabilities (p < 0.05). The current findings reveal RF to be a potential pretreatment for application in the industrial production of TPSO.

Effect of freezing and radiofrequency pretreatments on quality and kinetics of convective air‐drying of potatoes

The effects of freezing and radiofrequency (RF) pretreatments on drying kinetics and qualitative properties of hot air-dried potatoes were evaluated. Results showed that the use of an RF pretreatment before potatoes drying reduced the color changes, firmness, and increased shrinkage, rehydration ratio, and the effective diffusion coefficient. Whereas, the amount of activation energy was reduced by applying freezing and RF pretreatments. So that the amount of activation energy from 28.82 ± 0.4 kJ/mol (control sample) to 22.84 ± 0.1 kJ/mol (sample treated with CF), and 19.93 ± 0.2 kJ/mol (sample treated with CF and RF) decreased. The Henderson-Pubis model with the highest R2 and the lowest RMSE and χ2 was selected as the best model. Freezing pretreatment has weakened the tissue and created cell holes in the samples. When using RF, the amount of damage to the cell wall is greater, which makes the samples have a more porous structure using scanning electron microscopy. Practical applications Potatoes are one of the four main foods of the people of the world. Most of the potatoes produced are stored for use in the food industry. Due to the problems of storage, transportation, and seasonality of potato production, drying can be used as a suitable method to reduce potato waste. The most common method of drying is the use of hot air drying, which involves the simultaneous transfer of mass and heat. Since hot air drying uses high temperatures or long time, which in addition to high energy consumption and time-consuming process, causes some undesirable physical and chemical changes such as changes in color, flavor, and reduction of nutrients and shrinkage in the product. Therefore, using other drying methods or using pretreatment, the quality of the dried product can be maintained in a desirable. So far no research has been done on the use of CF and RF as a pretreatment in the potato drying. Therefore, the aim of this study was to investigate the effect of freezing pretreatments on drying kinetics and quality characteristics of hot air-dried potatoes.

Microwave pretreated enzymatic retting of flax stems and comparison with the effect of radio frequency pretreatment

Microwave (MW) together with prior water presoaking was used as a pretreatment for enzymatic retting of flax stems in this work. Weight loss, pectin removal, the resulting fibers’ properties and the degree of water absorption of the stems after MW pretreatment were measured and analyzed. The effect of MW pretreatment on enzymatic retting was determined and compared with the radio frequency (RF) pretreatment which adopted the same processing parameters. It was found that the 8 h-30 min MW pretreatment improved the enzymatic retting efficiency most, increasing weight loss by 39 %, decreasing pectin content by 10.96 % compared to the control enzymatic retting and obtaining water sorption of 2.23, and produced fibers with reasonable tensile performance. Compared with RF pretreatment, MW pretreatment enabled flax to absorb more water and more energy then got more improvement in the retting efficiency. And the 30 min-MW treatment could improve pectin removal for the non-presoaked flax as compared to the control enzymatic retting, which was different from RF treatment. The enzyme-retted fibers with the same MW and RF pretreatments had close tensile properties, however, their values of the MW-pretreated fibers tended to be slightly lower. It was also found that the tensile performance of the pretreated, enzyme-retted fibers was linked to the amount of energy absorbed, the temperature-maintaining time proportion during MW or RF treatment, and whether the flax had been presoaked or not.

Radio frequency-assisted enzymatic extraction of anthocyanins from Akebia trifoliata (Thunb.) Koidz. flowers: Process optimization, structure, and bioactivity determination

Anthocyanins are active compounds with various biological activities and are abundant in Akebia trifoliata (Thunb.) Koidz flowers. To extract anthocyanins from the flowers more effectively, a novel procedure of radio frequency heating-assisted enzymatic extraction was proposed in this study. The extraction conditions were optimized using Plackett-Burman and Box-Behnken design. The optimal extraction conditions were enzyme ratio of cellulase and pectinase of 1:1, enzyme concentration of 1.0 %, ethanol concentration of 50 %, liquid-solid ratio of 50 mL/g, pH of 4, and radio frequency pretreatment at 40 °C for 10 min with electrode gap of 5 cm. The results showed that radio frequency assisted enzyme extraction exhibited the highest crude yields (26.55 %) and anthocyanin content (50.87 mg cyanidin-3-O-glucoside equivalents/100 g) compared with hot water, acidified ethanol and enzymatic (pectinase and cellulase) assisted extractions. This method was effective for achieving high 1, 1-diphenyl-2-picrylhydrazyl radical scavenging activity (385.03 Trolox equivalents/g extract), reducing power (361.85 Trolox equivalents/g extract) and tyrosinase inhibitory (14.67 kojic acid equivalents/g extract) activity as well as significant α-amylase inhibitory activity. Nine anthocyanins were identified and did not detect any significant compound degradation using the novel approach. Accordingly, the proposed radio frequency and cellulase/pectinase combined extraction of anthocyanins was efficient and rapid. This method holds great promise for extracting bioactive compounds from plants and fruits.

Effect of radio frequency pretreatment on enzymatic retting of flax stems and resulting fibers properties

Radio frequency (RF) pretreatment of different water-presoaking time and RF treatment durations was introduced into enzymatic retting. RF pretreatment was used to degrade non-cellulosic materials and encourage the fast water-absorbing and swelling of the polar components in flax phloem, thus loosen the interfaces between fibers and fiber bundles and facilitate enzymes penetration. Retting efficiency, the resulting fibers properties and the water sorption after RF pretreatment were measured. It was found that the 8h-30min RF pretreatment improved retting efficiency most, increasing weight loss by 47 % and decreasing pectin content by 7.87 % compared to the control enzymatic retting and obtaining water sorption of 2.19. The results RF treated presoaked and non-presoaked flax were found to be different. The RF treatment of 30 min for the non-presoaked stems did not cause any improvement in pectin removal with a percentage decrease in pectin content of -8.41 %. The reason probably was that partial pectic substances in the non-presoaked flax phloem were dried, hardened and compacted during RF treatment. It was also found that RF pretreatment improved fibers whiteness and tended to weaken fibers tensile performance, and how it affected the fibers tensile properties was closely linked to the RF pretreatment processing.

Production and characterisation of antioxidant peptides from sweet potato protein by enzymatic hydrolysis with radio frequency pretreatment

SummaryEffect of radio frequency (RF at 70, 80 and 90 °C) pretreatment on production and characterisation of sweet potato protein hydrolysates (SPPH) prepared using Alcalase (ALC), Protease (PRO) and the combination of ALC + PRO was investigated. RF highly improved degree of hydrolysis (DH) and enhanced antioxidant activity of all SPPH produced by ALC, PRO and the combination as compared to traditional water bath (WB) heating pretreatment (P &lt; 0.05). RF significantly increased molecular weight (MW) &lt;3 kDa peptide fraction from SPPH produced by ALC, and MW &lt;3 kDa peptide fraction from RF80‐ and RF90‐pretreated samples has higher antioxidant activity. Diverse peptides in MW &lt;3 kDa fractions with RF80 and RF90 pretreatments were identified using LC–QTOF–MS/MS, which matched the sequences of sporamins and contained antioxidant amino acids Trp, Tyr, Met, Phe and/or His. There is a great potential application of using SPPH in functional foods as a novel ingredient.

Comparison of Different Electricity-Based Thermal Pretreatment Methods for Enhanced Bioenergy Production from Municipal Sludge.

This paper presents results for a comprehensive study that compares the performance of three electricity-based thermal pretreatment methods for improving the effectiveness of anaerobic digestion (AD) to process municipal wastewater sludge. The study compares thermal pretreatment using conventional heating (CH), microwave (MW), and radio frequency (RF) heating techniques. The effectiveness of the pretreatment methods was assessed in terms of chemical oxygen demand (COD) and biopolymers solubilization, AD bioenergy production, input electrical energy, and overall net energy production of the sequential pretreatment/AD process. The heating applicators for the bench-scale testing consisted of a custom-built pressure-sealed heating vessel for CH experiments, an off-the-shelf programmable MW oven operating at a frequency of 2.45 GHz for MW heating experiments, and a newly developed 1 kW RF heating system operating at a frequency of 13.56 MHz for RF heating experiments. Under identical thermal profiles, all three thermal pretreatment methods achieved similar sludge disintegration in terms of COD and biopolymer solubilization as well as AD bioenergy production (p-value > 0.05). According to the energy assessment results, the application of CH and MW pretreatments resulted in overall negative energy production, while positive net energy production was obtained through the sequential pretreatment/AD process utilizing RF pretreatment.

Advanced anaerobic digestion of municipal sludge using a novel and energy-efficient radio frequency pretreatment system

Microwave (MW) sludge pretreatment systems are usually limited to a frequency of 2.45 GHz and the heating frequency is constrained by commercially available hardware. Studies using MW heating at this frequency have reported negative net energy balance (output energy as methane minus input electrical energy). This necessitates further research into more efficient thermal pretreatment technologies. In this research, a novel and highly efficient radio frequency (RF) pretreatment system at a frequency of 13.56 MHz was designed, implemented, and tested for the first time. The system was custom-designed based on the dielectric characteristics of thickened waste activated sludge (TWAS) to achieve a very efficient and uniform heating system. The effects of three factors including pretreatment method (RF vs. MW), final temperature (60, 90 and 120 °C), and stationary (holding) time (0, 1 and 2 h) on sludge solubilization and performance of mesophilic batch anaerobic digestion were evaluated simultaneously. Energy measurements were also made to compare the efficiency of the custom-designed RF and conventional MW heating systems. The differences in sludge disintegration (solubilization) using the RF and MW pretreatment systems were negligible (P > 0.05). No statistically significant difference was also observed between the two pretreatment systems in terms of mesophilic biogas production rate and extent (P > 0.05). The energy efficiency of the RF pretreatment system was measured between 67.3 and 95.5% for the temperature range of 25–120 °C which was significantly higher than that of the MW system efficiency which varied from 37 to 43%. Overall, the average input energy of the RF system was less than half of the energy consumed during the operation of the MW system to achieve a same target temperature. Considering the results of this research, the RF heating at a frequency of 13.56 MHz is suggested as an effective and energy-efficient technique for thermal hydrolysis of TWAS.

Production of polyhydroxybuyrate (PHB) from switchgrass pretreated with a radio frequency-assisted heating process

Effects of radio frequency (RF) heating as a biomass pretreatment process to generate hydrolysates for polyhydroxybuyrate (PHB) were evaluated in all production steps from pretreatment to enzymatic hydrolysis to fermentation. Switchgrass was pretreated under alkaline conditions with RF-assisted heating (traditional water bath (WB) heating as control) and subsequently enzymatically hydrolyzed. Fermentation was conducted with recombinant Escherichia coli strain for PHB production using the hydrolysates as carbon sources with or without yeast extract (YE) supplemented. Results indicated that the hydrolysates generated through RF pretreatment performed consistently better for PHB production than WB (50% higher PHB levels without YE). YE supplementation (up to 5 g/L) enhanced fermentation under all conditions and diminished the difference among performances of fermentations. When adding 2 g/L YE, PHB production increased by 200% and 80% for WB and RF hydrolysates, respectively. Supplementation of 5 g/L YE brought the final PHB concentration to be very close to each other for all three fermentation conditions. Compared to traditional heating process, the unique heating mechanism of RF generates harsher conditions (under regular pressure) to disrupt the biomass structure more completely and generate more nutrients for bacterial fermentation. RF was therefore proved to be an efficient process for biomass pretreatment.

Improvement of acetone–butanol–ethanol (ABE) production from switchgrass pretreated with a radio frequency-assisted heating process

Radio frequency (RF) heating assisted alkaline pretreatment was evaluated as an emerging technology to generate hydrolysates for acetone–butanol–ethanol (ABE) fermentation. Traditional water bath (WB) heating was utilized as a control. ABE fermentation was conducted with Clostridium beijerinckii 8052 using the hydrolysates as carbon sources with or without yeast extract (YE, as supplemented complex nitrogen sources). Results indicated that the hydrolysates generated through RF pretreatment (RFH) performed consistently better for ABE fermentation than the hydrolysates generated through WB (WBH), with or without yeast extract (YE) supplementation. Without YE addition, fermentation with RFH generated 50% higher ABE than that with WBH. YE supplementation (up to 5g/L) enhanced fermentation under all conditions and diminished the difference among performances of fermentations. ABE production with 1 and 2g/L YE supplementation increased by 15% and 107% than those without YE for WBH, while for RFH the increase were 1% and 55%, respectively. Supplementation of 5g/L YE brought the final solvent production to be very close to each other with either WBH or RFH. Therefore, we concluded that RFH contained more nutrients than WBH which made a big difference for the ABE fermentation. RF could be explored as an efficient method for biomass pretreatment. This study provided valuable references for developing a sustainable system to convert lignocellulosic biomass into bioenergy in an economically efficient manner.

Effect of Radio Frequency Assisted Thermal Processing on Quality and Functional Properties of Egg White Powder

Abstract. Traditionally, egg white powder (EWP) is stored in a hot room maintained at 58°C to 60°C for 10 to 14 days for pasteurization and to improve functional properties. This long and energy-intensive process limits plant production capacity. In this study, radio frequency (RF) assisted thermal processing was evaluated for pasteurization of EWP with the objective of reducing the storage period in a hot room, thereby reducing the energy requirement, while minimizing loss of functional properties. Spray-dried EWP (pH ~9.5) was RF heated to 60°C, 70°C, 80°C, or 90°C and maintained at the same temperature for different storage periods ranging from 1 h at 90°C to 3 days at 60°C in a hot air oven. The quality and functional properties of the RF-treated EWP, including color, foaming capacity (overrun), foam stability, solubility, gel firmness, and gel elasticity, were evaluated. RF pretreatment of EWP at 90°C followed by holding in a hot air oven for 8 to 24 h provided optimal functional properties. RF-assisted thermal treatment at all levels did not significantly reduce the color lightness (L* values), solubility (Haenni value), and moisture content when compared to traditionally processed EWP. However, RF-pretreated EWP had a significantly lower foaming capacity (overrun) when compared to traditionally processed EWP. It was found that RF pretreatment at 90°C and holding in a hot air oven for 8 h or longer resulted in similar foam stability, water holding capacity, gel firmness, and gel elasticity. Therefore, we recommend RF heating of EWP to 90°C followed by holding in a hot air oven for 8 h or longer to produce similar or better functional properties compared to traditionally processed EWP. This treatment process is estimated to achieve ≥7-log reduction of Salmonella spp. Thus, RF-assisted thermal treatment can be used to reduce the pasteurization duration from the current 10 to 14 days to less than 24 h. We demonstrated the feasibility of designing a high-temperature short-time (HTST) pasteurization process for EWP using RF-assisted thermal processing.

Alkali (NaOH) Pretreatment of Switchgrass by Radio Frequency-based Dielectric Heating

Radio-frequency (RF)-based dielectric heating was used in the alkali (NaOH) pretreatment of switchgrass to enhance its enzymatic digestibility. Due to the unique features of RF heating (i.e., volumetric heat transfer, deep heat penetration of the samples, etc.), switchgrass could be treated on a large scale, high solid content, and uniform temperature profile. At 20% solid content, RF-assisted alkali pretreatment (at 0.1 g NaOH/g biomass loading and 90 degrees C) resulted in a higher xylose yield than the conventional heating pretreatment. The enzymatic hydrolysis of RF-treated solids led to a higher glucose yield than the corresponding value obtained from conventional heating treatment. When the solid content exceeded 25%, conventional heating could not handle this high-solid sample due to the loss of fluidity, poor mixing, and heating transfer of the samples. As a result, there was a significantly lower sugar yield, but the sugar yield of the RF-based pretreatment process was still maintained at high levels. Furthermore, the optimal particle size and alkali loading in the RF pretreatment was determined as 0.25-0.50 mm and 0.25 g NaOH/g biomass, respectively. At alkali loading of 0.20-0.25 g NaOH/g biomass, heating temperature of 90(o)C, and solid content of 20%, the glucose, xylose, and total sugar yield from the combined RF pretreatment and the enzymatic hydrolysis were 25.3, 21.2, and 46.5 g/g biomass, respectively.

Radio-frequency ablation increases intratumoral liposomal doxorubicin accumulation in a rat breast tumor model.

To determine whether intratumoral accumulation of liposomal doxorubicin or free unencapsulated doxorubicin is increased when combined with radio-frequency (RF) ablation. Two 1.2-1.5-cm R3230 mammary adenocarcinomas were grown within the mammary fat pads of 19 female Fischer rats. One tumor of each pair was treated with RF ablation (tip temperature, 70 degrees C +/- 2 [SD]; 120 mA +/- 75) for 5 minutes, whereas the other tumor was a control. Intravenous liposomal doxorubicin (1 mg in 500 micro L, n = 6) or intravenous free unencapsulated doxorubicin (n = 7) was administered immediately following RF ablation. Doxorubicin was extracted in acid alcohol from tumors 24 hours following RF ablation, and fluorescent spectrophotometry was used to quantify extracted doxorubicin. Comparisons of intratumoral doxorubicin accumulation in tumors treated with RF ablation and in untreated tumors were analyzed with parametric (paired Student t test) and nonparametric (Wilcoxon rank sum test) statistics. Findings at autoradiography with densitometry (six additional tumors) demonstrated the spatial distribution of the intratumoral accumulation of liposomal doxorubicin. When RF ablation preceded administration of liposomal doxorubicin, mean intratumoral doxorubicin concentration was 5.6 micro g/g +/- 2.1 (range, 1.9-7.7 micro g/g), whereas 1.0 micro g/g +/- 0.4 (range, 0.5-1.5 micro g/g) was present in control tumors not treated with RF ablation (P <.05). Thus, there was a mean 7.1-fold +/- 4.9 increase in intratumoral doxorubicin accumulation following RF ablation (range, 2.1-14.5-fold) compared with the amount without RF pretreatment (P <.05). Increased intratumoral accumulation was not seen in animals receiving free doxorubicin with (mean, 0.4 micro g/g +/- 0.1) or without (mean, 0.8 micro g/g +/- 0.4) RF pretreatment (P =.07). Autoradiographic findings demonstrated accumulation of liposomal doxorubicin in a peripheral rim of tumor adjacent to the zone of coagulation. RF ablation augments the delivery of systemic antineoplastic agents such as liposomal doxorubicin.

Adhesion of colloidal ZnS on silicon. Effects of ionic strength and radio frequency electric field

The adhesion of zinc sulfide particles to silicon plates in the presence of aqueous solutions of several electrolytes, NaCl, MgCl2, and LaCl3, has been studied. The results are discussed in the light of the extended DLVO approach, in terms of energy-balance plots versus the distance between the interacting surfaces. Moreover, we were also interested in finding out whether high-frequency (43 MHz) electric field pretreatment of the surface influenced the adhesion process. The adhesion of ZnS was quite dependent on the NaCl concentration, being higher as the concentration of NaCl was increased. The effect of applying a radio frequency (RF) electric field during the adhesion process was only noticeable at the lowest NaCl concentration studied (0.1 mM). RF pretreatment in such conditions reduced the adhesion of ZnS to Si. The type of counterion in the solution determined the surface properties of both the adherent and the substrate. The results using 1 mM NaCl, MgCl2, and LaCl3 aqueous solutions showed that th...